Personal communications service (PCS) generically describes a form of wireless telephone communication having the characteristics of low power, short range, and low cost. It is envisioned that PCS will economically compete with both cellular radiotelephone services and wireline telephone services. For a general overview of PCS type services and equipment see "Personal Wireless" by Bennett Z. Kobb, IEEE Spectrum June 1993, pages 21-25.
Several concepts of multiply-tiered services for PCS customers have been advanced. One key discriminator among the various service tiers is the degree of mobility accommodated by each of the tiers. A basic two service tier would include "local" service and "enhanced" service. Both provide complete wireless telephony for voice and low speed data, voice mail, and short message services. Local service is conventionally restricted to radio coverage provided in selected geographic subregions--public/private, indoor/outdoor--of a total PCS service area. This service is configured to provide "pedestrian" stowice to portables. Enhanced service conventionally includes the local service plus an additional "cellular-like" service to accommodate vehicle-borne portable units moving at moderate or high speeds. Enhanced service subscribers conventionally require dual mode portables. Full mobility for either service is desirable and would include inter-system handoff and local, regional, national, and international roaming among various interconnected systems using a standard intersystem protocol. Realizing such a wide area of mobility, however, necessitates the addition of expensive network elements to a conventional wireline telephone system. Such network elements are location registers, specially programmed telephone exchanges, and telephony signaling networks. It is desirable that automatic delivery of incoming calls be achieved regardless of the subscribers current location.
The fixed Public Switched Telephone Network (PSTN) in the U.S. basically consists of a large number of telephone switching offices interconnected with one another by means of interoffice trunks. Connected to the telephone network is a very large number of customers, each of whom has a telephone set that is connected to one specific telephone switching office (end office) by a particular physical set of wires or their equivalent that go from the customer's telephone set to the end office. For this fixed network a numbering plan is employed in the U.S. by which each telephone line (each "local loop") is identified by a particular number. This number has a geographical significance in the sense that it is structured to have an area code which localizes it to a particular area of the country, an office code which localizes the number further to a particular end office switching system, and a line code which localizes it finally to a specific line appearance on that end office. The entire network is arranged so that whenever a particular line indicates a customer's request for service (an ON-HOOK to OFF-HOOK transition), the end office to which the line is connected recognizes who the customer is (for billing purposes), where the customer is, and what kind of services are authorized for the customer's particular line. This procedure is called "call origination". Dialled digits that are received from the line for a call are recognized by the end office as indicating a particular outgoing route based on the area code and office code combination. The call is routed step by step in this fashion through the network until it reaches the far end where the destination end office recognizes the dialled area code, office code, and line code combination as representing a local loop connected to it. This procedure is called "call routing". The called line is then alerted (rung) and when the called party answers (OFF-HOOK) the final connection for the call can then be made. This procedure is called "call termination".
Thus, every telephone has a line or a local loop that has a number which uniquely identifies it. It is conventional logic in the telephone network that every telephone stays fixed and attached to its particular line appearance and does not move around. A local loop, conventionally, does not provide for customer mobility.
Cellular or mobile telephone service enables customers to have telephone sets (radiotelephones) that are not attached by wires to an end office. There is no office anywhere that has a line appearance that is recognized as being associated with the number of that radiotelephone. This means that most of the end user offices in the North American fixed telephone network are not able to deal with mobile telephones. The fixed end offices are not equipped for customers and telephone sets that are not attached to one specific fixed line appearance all of the time. Since conventional end offices cannot identify calling parties, route calls, do billing, or provide services and features except on the basis of fixed local loops, special switching systems, called mobile telephone switching offices (MTSO), are designed with special software and special hardware to interwork with each other via a suitable signalling network to accommodate customer mobility. The MTSOs also interface with the rest of the fixed telephone network, usually on a trunked basis, and thus constitute a mobile telephone network separate from but ancillary to the PSTN. With this equipment, customers and their radiotelephones can move around from one place to another, from one part of the country to another, from one city to another, and from one system to another.
To facilitate this mobility, standards have been devised (Air Interface Specifications) by which the radiotelephones can identify themselves to whatever mobile telephone system in which they find themselves. The system can then interwork through a suitable signalling network with other elements of the mobile telephone network to identify the customer, validate the customer's ability to get service, and record the network location of the customer at the moment.
If the called radiotelephone's current recorded network location is determined to be the originating MTSO, then that MTSO must execute a call termination procedure that includes determining whether or not the radiotelephone is in service, establishing contact with the radiotelephone and assigning it to a radio channel, alerting the radiotelephone user and, if an answer is received, making the final connection. However, if the radiotelephone's current recorded network location is not the originating MTSO, then the routing procedure must be extended to establish a connection with the current serving MTSO where the radiotelephone is located and that MTSO must execute the call termination procedure.
Thus, there is a clear network difference between a customer who is served by a fixed local loop where his telephone set is always found at the end of wire-like connections in the end office and a customer who is served by a radiotelephone which is dynamically changing locations, a consequence of which is that no local loop nor its associated advantages is present for the radiotelephone customer. Since a personal communications service (PCS) is a service which closely associates a telephone number with a customer, it would be desirable that a PCS stowice offer the advantages of both a local loop service and mobile telephone stowice without the added expense of additional network elements to obtain customer mobility.